Invasive algae starry stonewort affects Minnesota lakes

[USA] Minnesota lakes are invaded by starry stonewort,  an invasive species of  algae that is dangerous both for the native lake weed and the fish that live in the lake.

On Friday the Minnesota Department of Natural Resources has announced that the invasive algae was found in two connected lakes near Paynesville: Mud and Koronis. It seems that starry stonewort,   has been there for quite a long time. It was initially covering 53 acres of  a southwest area of Lake Koronis and afterwards it spread into the main basin and reached Mud Lake as well.  The invasive plant behaves similarly to Eurasian milfoil: it grows in dense mats which cover the surface of shallow waters. As a consequence it does not only squeeze out other plants but it also prevents fish from reaching their spawning grounds.

According to Chip Welling who is an invasive species coordinator from the DNR said that it took quite some time for experts to confirm that the plant was starry stonewort.  It seems that the property owners on the lake have been struggling with it for some time before the Lake Association announced DNR once the plants began to smell. Karen Langmo from the Koronis Lake Association said that the lake is sacred to her and it is hard for her to see what is going on with it.

Starry stonewort got its name from its bulbils that have the shape of a star. The algae was discovered in 1986 in Lake St. Clair and it had spread widely in Michigan.  Last year it was discovered for the first time in Wisconsin. According to Welling the plant most likely reached Minnesota lakes from a bot which probably picked up a fragment of the plant from another lake where starry stonewort can be found.

It seems that the plant is native to Europe and even endangered in England. It most likely reached the great Lakes watershed through ballast water discharged from freighters.

Langmo believes that this is a lesson for careless boat owners who must pay more attention to the protection of other lakes in the state.


Note: Charales is an order of freshwater green algae in the division Charophyta commonly known as “stoneworts”. Linnaeus established the genus Chara in 1753. The Charales have large, macroscopic thalli growing up to 120 cm long, they are branched, multicellular, and use chlorophyll to photosynthesize. They grow in fresh water. Stonewort is not a plant.

Photo: Starry stonewort does not only squeeze out other plants but it also prevents fish from reaching their spawning grounds.

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